An outdoor unit, which configures an air conditioner with an indoor unit, includes a compressor that compresses a refrigerant. The compressor is driven by a motor under the control of a microcomputer that controls the operation of the outdoor unit.
The outdoor unit individually needs a power supply circuit (hereinafter, referred to as a “main power supply circuit”) such as an inverter for driving the motor and a power supply circuit (hereinafter, referred to as an “auxiliary power supply circuit”) that drives the microcomputer. This is because the motor may stop during the operation of the microcomputer in the outdoor unit.
Thus, a DC voltage (hereinafter, referred to as a “main DC voltage”) to be supplied to the main power supply circuit and a DC voltage (hereinafter, referred to as an “auxiliary DC voltage”) to be supplied to the auxiliary power supply circuit are generated individually.
In such a situation that the operation of the compressor is not necessary or is inappropriate during the operation of the air conditioner (hereinafter, referred to as a “compressor-stopped situation”), a supply of an auxiliary DC voltage is kept with a supply of a main DC voltage stopped, thereby controlling or protecting the outdoor unit by the microcomputer.
Examples of the case in which the operation of a compressor is not necessary include the time immediately after the start of an air conditioner and the time during an air conditioning operation (so-called “thermo-off”) in which a compressor needs not to be driven. Examples of the case in which the operation of a compressor is inappropriate include the times in which an overvoltage occurs in a main DC voltage, an overcurrent flows through a motor, and the load of a motor becomes excessive.
In compressor-stopped situations other than the case in which an overvoltage occurs in a main DC voltage, it is desirable to keep sensing whether an overvoltage occurs in the main DC voltage by keeping a supply of an auxiliary DC voltage with a supply of the main DC voltage stopped.
As described above, a main DC voltage and an auxiliary DC voltage are required individually, and the former is interrupted in the compressor-stopped situation. Upon such a request, which is one of the factors, a main DC voltage and an auxiliary DC voltage are generated by individual rectifier circuits (hereinafter, which are respectively referred to as a “main rectifier circuit” and an “auxiliary rectifier circuit”).
Meanwhile, for the reason of design, such as fewer parts, a main DC voltage and an auxiliary DC voltage are generated by a common AC power supply. Then, to stop a supply of the main DC voltage and keep a supply of the auxiliary DC voltage even in a compressor-stopped situation, a power switch is provided to the AC input side of the main rectifier circuit. In contrast, an AC voltage is input to the AC input side of the auxiliary rectifier circuit while bypassing the power switch.
In the known techniques, as described above, the common AC power supply feeds power to the main power supply circuit through the power switch and to the auxiliary power supply circuit while bypassing the power switch. For example, Japanese Patent Application Laid-Open No. 2000-111123 describes and illustrates such a technique.
Japanese Patent Application Laid-Open No. 2000-69786, Japanese Patent Application Laid-Open No. 2011-10494 and Japanese Patent Application Laid-Open No. 08-79963 (1996) are cited here as the prior art documents that describe and illustrate an overvoltage detection circuit. In addition, Sekimoto and four others, “Development of Air Conditioner Compliant to IEC Harmonic Standard by Single-Phase to Three Phase Converter without Electrolytic Capacitors,” IEEJ Technical Meeting on Motor Drive, No. MD-11, pp. 51-56 (2011) is cited as the prior art documents that describe the control of a so-called inverter without electrolytic capacitor.